Various model retinals are being synthesized and bound to cattle opsin to give model visual pigments which clarify specific points of the visual pigment structure and the transduction process. Studies with opsin from squid and other animals will be carried out to check our external point-charge model, which was proposed to account for the wide variation in absorption maxima, 460-630 nm, of various visual pigments. A photoaffinity labeled visual pigment has been prepared. Studies with such pigments will clarify the binding site structure of rhodopsins.